Jumping on water: Water strider shows the way

The robot jumper starts to jump: Notice the "dimples" as it exerts downward force on the water. Surface tension prevents it from breaking the surface.

Seoul National University

Nature, through evolution, is the ultimate problem solver. Need to kill microbes? Check out the elaborate and adaptive immune system. Need to fly? Countless thousands of critters have solved that, even including some mammals (the bats).

Need to walk on water? A few animals, including the water strider and some reptiles, can do that.

Need to jump on water? That's select territory. One of the few animals with that talent is the water strider.

Now, researchers in South Korea have figured out the strider's secret -- and used their understanding to build a life-size model that, like the strider itself, lifts off and then splashes down with a catawampus belly-flop.

The strider jumps to avoid danger. The Korean creation, designed by Seoul National University's Ho Young Kim and Kyu Jin Cho, jumps to impress humans.

The all-organic, biologically designed water strider not only walks on water -- it jumps on water!

And it does. Witness the article in this week's edition of the journal Science1

We have liftoff!

To jump clear of the water, the strider (and the robot) must exert a force on the water that overcomes gravity. To do this, the jumper exploits surface tension -- the elastic quality of a liquid surface resulting from the strong cohesion between water molecules.

When a strider supports its weight, it creates dimples in the water. In response, surface tension pushes upward as the water "tries" to reduce its surface area and flatten out.

Push too hard, of course, and the foot goes right through the water, and the jump fails, so the water strider has evolved to push hard enough and long enough to leave the water surface, without punching through it.

And that, in a nutshell, is what the Korean researchers have recreated with their 68 milligram wonder.

The robot jumps, in ultra-slow-mo (1/200 of actual speed). Notice absence of splashing; feet are dry as they leave the water.

Seoul National University

What does it take?

The physical elements the robot would need were evident in high-speed video of a water strider:

A propulsion system that gradually increases force on the legs -- to avoid punching through the surface.

A sweeping motion of the legs that extends the duration of the downward push to maximize total lift.

A curved "foot" that exploits surface tension through the entire stroke.

A water-repellant surface on the legs, so all water drops away during the launch.

A manufacturing technology based on paper-folding techniques that creates light-weight structures with ultra-low friction hinges.

A video explains the research process and its implications.

Credit: Carla Schaffer/AAAS

As proof of their principle, the robot jumped just as high on water as on a hard surface.

According to a prepared statement by the authors, the organic water strider approaches perfection. "Based on a theoretical model of a flexible cylinder floating on liquid, the authors found that the maximum force of the water striders’ legs is always just below the maximum force that water surface tension can withstand. In fact, surface tension on the four legs was 16 times the robot's weight, giving plenty of scope for enough added force to launch the robot into the air."

By regulating the motive spring in their robot, they achieved much the same result -- although the robot strider, unlike the organic version, is not yet able to walk on water.

"This robotic technology could probably be used for building a large number of robots that can float, and jump on water for surveillance missions," the authors added. "However, this study did not begin with an intent to create a real world application. We were fascinated by the fact that insects can actually jump on water quite well, something that humans or any engineered system cannot replicate."

Australian "dragon." If it's hot, eggs hatch with female genitalia but male genetics.

The Australian central bearded dragon is widespread in the semi-arid open woodlands of eastern Australia. They feed on leaves, fruits and insects and spend most of their time in shrubs or trees. They also make a popular house pet due to their hardiness.

Photo: Arthur Georges

As if climate change doesn’t bring enough to worry about, now comes word that it's affecting the sex of newborn lizards in Australia, and could even make males extinct.

"A boy or a girl?" is the classic post-partum question. In humans and other mammals, the choice is made by the sperm that penetrates the egg. If it carries a Y chromosome, "It's a boy!" Otherwise, "It's a girl!"

This is called genotypic sex determination.

We've just learned it's a different story in reptiles. In some, the sex of the offspring depends on the egg's incubation temperature. So-called temperature sex determination (TSD) means that reptiles with female genitals carry male (called ZZ) chromosomes.

That transformation has been seen in several species in the lab. Now, for the first time, scientists have found the phenomenon in the semi-arid outback of Australia, in the Australian central bearded dragons (Pogona vitticeps).1

The Australian central bearded dragon was trapped in these areas in the open woodlands of Eastern Australia.

Modified by The Why Files

Leapin' lizards: Where have all the guys gone?

This real-world find comes with a twist of major ecological significance: If temperatures remain high, ZZ females could predominate. In other words, guys could eventually go extinct, and with them, the entire population of these dragons.

It's not clear whether TSD confers an evolutionary advantage, but the authors found signs that the process could become self-perpetuating: the offspring of ZZ females are more likely to become ZZ females. And those sex-reversed mothers lay nearly twice as many eggs per year as normal mothers, leading to more feminized populations.

Should we worry that the population will expire for lack of males? "That is true," corresponding author Arthur Georges of the University of Canberra wrote us.

When genes determine sex, ZZ equals male and ZW equals female. "Our research shows a transition from a ZZ/ZW population to a pure ZZ population over relatively few generations," Georges said. "The W [female] sex chromosome is jettisoned."

But that's not necessarily a dead end. "What rescues the population is that some of these ZZ individuals would be reversed to females," he added. "So there would still be both males and females even if the W chromosome is lost to the population." But if temperatures continue to rise, "We could find that only females are produced and the population would crash" for lack of males, even though they carry the ZZ genes.

Extreme heat waves are not uncommon in present-day Australia. According to the Bureau of Meteorology, half of the biggest heat waves (where average Australian temps soared to the hottest 99th percentile) of the last century occurred just in the last two decades.

To test whether TSD was taking place in the wild, the researchers captured 131 dragons between 2003 and 2011 and found that 20 percent them were ZZ females. The numbers showed a non-significant trend toward feminization that paralleled rising temperatures. Another possibility – perhaps also linked to warming – the loss of vegetation may expose the nests to more sunlight, leading to more poached (heh heh!) eggs.

Reproductive reptiles: It's a real zoo!

We confess that we'd given the subject little thought, but Georges wrote to say that "Reptiles have an astonishing number of ways of determining the sex of their offspring." Some use the human system (relying on father's chromosomes), others rely on the mother's. He mentions many alternatives:

The Australian central bearded dragon perches on trees or rocks to bask in the Australian sun. Extreme heat during incubation can turn the offspring female -- even if they have male genes.

Arthur Georges

Parthenogenic reptile species "have done away with males altogether, with the females engaging in virgin birth" from an unfertilized egg;

Facultative parthenogenesis is an optional variant: females deprived of males can spawn male offspring, "a great benefit to sole invaders of isolated islands;"

"Many turtles, all crocodiles, some reptiles and New Zealand’s tuatara, have dispensed with genetics and incubation temperature alone determines offspring sex."

"Just when scientists thought they had a handle on all this, the Australian Central Bearded Dragon has delivered another surprise," Georges says, a single species can show that there is more than one system for controlling sex.

“The emerging picture is that reptilian sex determination is more flexible on an evolutionary scale than could ever have been imagined," commented2 James Bull of the University of Texas in Nature: “... chromosomal and environmental sex determination can both be highly functional, adaptive systems ... that are alternative states that could, in theory, evolve back and forth."

The new study shows “how quickly such a substantial evolutionary change can occur in response to a rather modest shift in climate," Georges wrote to us. “We are used to hearing that evolutionary change is too slow to be an effective response to the rapid and unprecedented climate change we are currently causing on Earth. It seems that there are after all opportunities for very rapid evolutionary responses, such as changing one’s mode of sex determination."

How baboons decide

Seen resting in the shade, this troop of Kenyan baboons was tracked to show the group dynamics related to route choices.

Photo: Rob Nelson

Baboons live in highly structured groups gathering fruits, nuts, even meat. The alpha male gets the females, until he is deposed by a younger competitor. So we were surprised to learn that when they forage across the countryside in Kenya, their decisions are "democratic."

If Roger moves North and Alice moves northeast, Sandra is likely to split the difference, and head north-northeast.

But if Ann joins Roger both move to the north, Sandra will follow them.

If Paul moves North and Jean moves South, Sandra may follow either one.

These results (but not the plain-Jane American names) come from a new study1 of wild baboons, conducted with the help of high-precision GPS collars, by Margaret Crofoot, an associate professor of anthropology at the University of California-Davis.

Researchers watch the baboon troop forage. About 80 percent of the adults and sub-adults were fitted with high-accuracy GPS collars. Data were collected from 25 individuals, every daylight second for 14 days.

Photo: Rob Nelson

The researchers establish standards for a "pull" (when Clara moves at least 5 meters, and Stephen, nearby, follows) and an "anchor" (when Stephen fails to follow Clara). "Our algorithm looks at the change in distance between two individuals," says Crofoot. "We are looking purely at movement; there is no behavioral data."

We WhyFilers were shocked that the research produced no sign that social status determined who has pull and who doesn’t. According to the authors, "The dominant male did not have the highest probability of being followed, dominance rank did not correlate with initiation success, and no sex differences existed in initiation success.'

When we asked Crofoot, she told us, "Dominance confers first access to food and monopolizes mating access for males, so I was a little bit surprised that we did not find more evidence of a dominant individual using that social power to drive group movement to their advantage.

Previous experiments on primate social decision making were carried out in captivity, she says. "This was the first one in a relevant ecological and social context. Our study highlighted that even if the dominant individual can determine group movement in specific circumstances, most of the time, it's a more democratic process," she added. "As they travel through the habitat … mostly they have an egalitarian, majority rule aspect."

We commented that the baboon behavior seemed highly logical. "Part of what is incredible about this study it that it jibes with the experience we have all had in trying a get a group of people to make a decision when opinions diverge strongly," Crofoot said. "That can stall a group decision so you can't come to any decision, but when the difference between potential choices is small, you can split the difference and push the decision further down the read."

To capture the entire baboon troop, the researchers operated as many as 22 cage traps at once. They hand-triggered the trap doors to avoid recapturing animals that already had a GPS collar, and to ensure that mothers and their offspring were not separated.

Photo: Rob Nelson

Like fish, like birds?

Our conversation was going swimmingly until Crofoot brought up a resemblance to similar decision-making among schools of fish and flocks of birds. Surprisingly, the baboon "results match quite closely with models designed to understand fish movement" Crofoot says. "The majority rules, you split the difference rather than choose between close angles. I was struck by the similarity."

People are a bit more complicated than fish or blackbirds, Crofoot acknowledged. "Human societies have all this stratification, dominance hierarchy, kinship, friendship, various other social relationships, and baboons are a really good system for trying to bridge that gap, because they have dominance, strong kinship, 'friendships' involving preferred social partners."

Eurasia's genetic landscape unraveled

This Yamnaya skull from the Samara region, north of the Caspian Sea in Russia, was colored with red ochre.

Credit: Natalia Shishlina.

After an unprecedented genetic analysis of ancient human specimens from Europe and Asia, archeologists have pinned many modern genetic and linguistic patterns across the region on the Yamnaya, a poorly known population that originated in Central Asia.

The study explains a number of mysteries, says corresponding author Eske Willerslev of the University of Copenhagen.

What were the major influences for the broadest genetic patterns in Eurasia?

Were the massive economic and cultural changes during the Bronze Age due primarily to the movement of people or of ideas?

Why do so many people across Europe and Asia speak the related "Indo-European" languages?

Why is the globally rare ability to drink unprocessed milk so common in Northern Europe?

Good results require good data, and Willerslev says the group used new methods to extract human DNA while excluding the microbial DNA that contaminates it. "After death all parts of the body are filled up with microorganisms, so in the range of 95-99 percent of DNA is not human."

To address their questions, the research group sequenced the genomes of 101 individuals from Europe and Asia during the Bronze Age (5,000 to 2,000 years ago). That was about five times the previous number of archeological genome sequences from the region, Willerslev says.

Keep on truckin'!

The genetics proved that "the Bronze Age involved massive population movement, so there is no doubt that these cultural changes also involved the movement of people," Willerslev says.

New genetic sequencing shows the expansion of the Yamnaya culture from central Asia. "By 2800 BC a new social and economic formation, variously named Corded Ware, Single Grave or Battle Axe cultures developed in temperate Europe, possibly deriving from the Yamnaya background, and culturally replacing the remaining Neolithic farmer."1

The Yamnaya originated in the northern Caucasus, and spread into central and northern Europe, where they mixed with locals. At the same time, they also spread into central Asia, to western China, southern Siberia and Mongolia, Willerslev says. "This fits beautifully with the distribution of the Indo-European languages, and it's very tempting and reasonable -- there is no direct proof -- to argue that the Indo-European language spread with the Yamnaya people."

The world's languages

Indo-European languages are spoken by almost 3 billion native speakers, the largest number by far for any recognized language family. Of the 20 languages with the largest numbers of native speakers according to Ethnologue, 11 are Indo-European: Spanish, English, Hindi, Portuguese, Bengali, Russian, Punjabi, German, French, Marathi, and Urdu, accounting for over 1.7 billion native speakers. (Source: Wikipedia.)

During the Bronze Age, the human genetics of northern and southern Europe diverged, mainly due to the arrival of the Yamnaya in Northern Europe, on a route that bypassed Southern Europe.

Migrations during the Bronze Age by and large created the current Eurasian genetic picture by 2,000 years ago, Willerslev says. By then, "the genetic landscape resembles to a large extent what we see in Europe and Asia today. But in the early Bronze Age, it does not. The majority of genetic differences, the distribution of people that we see in Central Asia and Europe today, were set during the Bronze Age."

The biggest surprise was in Central Asia, where four population replacements occurred in just 3,000 years. "It's the most dynamic place I have ever heard about in human history," Willerslev says. "It's quite mind blowing."

It's uncertain whether any close descendants of Yamnaya remain in central Asia, Willerslev says. "This remains to be investigated. In northern Pakistan, you do have people with very blondish hair and blue eyes who might be descendants of the Yamnaya, or of other Europeans who entered central Asia during the Bronze Age, but this is speculation."

These barrows, built from about 3,500 to 3,100 years before present, are typical of Bronze Age barrows in Denmark. Barrows were built by ancient cultures to bury the dead or for other ceremonial purposes.

Credit: Kristian Kristiansen

Migrations, culture, and upheaval

The upheaval that followed the arrival of the Yamnaya in Central Asia may have exceeded the transformation that followed European colonization of the Americas. "The Central Asians were hunter-gatherers who had stone tools and weapons," Willerslev says, "and the Yamnaya suddenly came in with horses, wagons, wheels, bronze weapons instead of stone. They are bringing in completely new technologies."

The "corded ware" cultures of northern Europe were influenced by the arrival of Yamnaya immigrants starting about 5,000 years ago. This corded-ware pottery in the Museum für Vor- und Frühgeschichte (Berlin), from about 2500 BC.

The Yamnaya's effects were less striking in northern Europe, which was already populated by farmers, Willerslev says, "but the Yamnaya did change the way they buried their dead, changed the material they used for creating tools and weapons, and the type of housing and family structure."

And they may have brought the gene for the enzyme that digests lactose, the sugar in milk.

The new genetic study indicates that the migrants were breeding with the residents in northern Europe. In contrast, changes in central Asia during the early and middle Bronze Age were "extremely abrupt," Willerslev says, "and could be due to war, disease or climate change."

The broadest goal of the study was to shed light on how technology and culture spread, Willerslev says. "This has been a big debate with two extremes. On the one hand, you have people saying this was all due to the transmission of ideas, not human movement. At the other extreme, archeologists say it involved really massive people movements. Our data is in agreement with the latter."

The Yamnaya shaped the very way we are communicating about these events, Willerslev says. "The Indo-European language was a Yamnaya invention, and it spread with them. They were genetically successful in the early Bronze Age, 5,000 years ago. At that time, we would talk about them as we talk about the Chinese today, spreading across world very successfully."

Sleep: It can enhance memories!

A lesson on hysteria by André Brouillet,1887. For centuries, sleep and sleep-like states have been exploited for therapeutic, neurologic (and sometimes insidious) gains. This painting, which Sigmund Freud took back with him to Vienna following studies with Jean Martin Charcot, shows Charcot (to the right of the hypnotized woman), pioneer of neurology at the hospital ‘la Salpetriere’ in Paris.

Erich Lessing/Art Resource, NY

Take a nap with certain sound clips playing softly, and emerge a better person? Seems too good to be true… But we have just read about a quick-fix for sexist and racist bias built around a 90 minute nap. While sleep-learning has sometimes been portrayed as brainwashing, the process we're describing may be closer to brain-cleaning.

In a study published in this week's Science, Xiaoqing Hu, a postdoctoral fellow in the Social Cognition Lab at the University of Texas, Austin, and colleagues attempted to reduce sexist or racist bias by presenting an image of a women, or a black person, paired with a counter-stereotypical word. Subjects were asked to press a button only if the face was paired with a science-relevant word or a positive word.

If they got the right answer quickly enough, they heard a sound when they pressed the button.

Tests afterward revealed that this conditioning reduced bias. But here's the crazy part: Each subject took a 90 minute nap, and when they got into a deep sleep, they heard one of the sounds from the conditioning, on average, 258 times.

The study was designed to counter "implicit bias" revealed in the implicit association test. This psychological test demands quick responses and is designed to reveal socially unacceptable biases that are often unrecognized. When asked, "Are you prejudiced against black men?" most people will say no…

Implicit social bias can be reduced if sleep is used to reinforce a learned reduction in bias. A: Psychologists encouraged the participants to counter implicit bias by matching a "counterbiased" pair (for example, the face of a woman and the word "math"), followed by sound feedback. No sound feedback occurred if the participant selected the "biased" match, or if the “counterbias" match was too slow. B: Training included drag-and-drop exercise to match a face with the "counterbiased" word, with the same sound feedback as before. C: This sound was then repeated during the participants’ 90-minute nap to reactivate the memory formed during the counterbias training, leaving a lasting impression (D). Rollover image to a bar graph with error bars showing that playing the sound cue during the nap significantly reduced bias, even one week later. Not playing the sound during the nap led to a rise in bias after the nap.

We had a bunch of questions…

What follows is an edited version of our conversation with Hu.

Q: What is it about slow-wave sleep that makes this process work?

A: There are different stage of sleep: light, REM (rapid eye movement) and slow wave -- a deep sleep where the electroencephalograph shows very deep, slow oscillations. There is a lot of evidence that episodic memories -- memories of events -- are consolidated during slow wave. When a memory comes in, it's encoded in the hippocampus, but this is not stable. During slow wave sleep, the memory is transferred to the nearby neocortex, where storage is more stable. Evidence suggests that what is special about deep sleep is that these different brain regions start talking to each other, so memory can be consolidated.

Q: Is sleep necessary to the bias reduction?

A: We show that the initial session -- before the nap -- does counter the bias, so it's not just that sleep can help with learning or unlearning something unwanted. But the nap greatly strengthened the process. Without it, the change essentially vanished after a week.

A 1956 record cover of Aldous Huxley’s radio broadcast of Brave New World shows an infant trapped in a bubble manipulated by “Big Brother.” That Hu and colleagues demonstrate the effectiveness of conditioning the subconscious during sleep reminds us that this research needs to be guided by ethical considerations, according to a commentary in Science.1

A: During sleep, the auditory cue that was originally paired with learning can reactivate the learning and consolidate it. But even without that cue, a memory can be spontaneously reactivated during slow wave sleep; what we learn in the day will be consolidated in the evening. The advantage of our technique is that selecting the cue can select which memory to consolidate. A couple of prior studies used this technique to choose which memory to consolidate, but we were the first to use it to affect social memory, attitudes. The basic pattern, that you can cue memory, was seen before, but what was novel here was the use to affect implicit social bias. And because social bias comes from early experience, it's hard to change

Q: Would people agree to be reprogrammed with a method that's sometimes presented in movies as brainwashing, even if the goals socially acceptable?

A: This was done in the lab. People may not be able to use this directly in real life, but the principle here is that during sleep, you can reactivate learning that you want to consolidate. We can rehearse something that is important to us. If you think about an important memory and rehearse it before sleep, it's likely to be reactivated during sleep, that's been shown by previous research, and so the basic principle is still the same.

Q: Where else would this technique be used?

A: We can speculate it would be great while studying to play a sound in the background to create an association between the sound and learning. When you fall asleep, you could play that sound over and over. That may be helpful, but we need more data to know for sure. It might work with other types of unwanted bias, related to disability or sexuality. You could think of fear as a kind of unwanted memory, and there are other studies that have shown a reduction in fear during sleep.

Q: Are you weakening the original learning (the implicit bias) or strengthening a new learning (the association with positive thoughts)? Is this unlearning or learning?

A: Good question. I don't think our study can answer that one way or the other. Maybe it's some of both. By consolidating the new attitude or memory, that creates competition between it and the old attitude, so the old attitude will be weakened.

New species explore biological limits

The inch-long sea slug Phyllodesmium acanthorhinum is a "missing link" between sea slugs that feed on hydroids (small predators related to jellyfish) and on corals. This beauty lives in Japanese waters.

Photograph: Robert Bolland

About 18,000 species are named every year — adding to nearly 2 million that have already gotten a name. On May 21, the International Institute of Species Exploration at the SUNY College of Environmental Science and Forestry released its latest list of top-10 new species. As the institute said via press release, the goal is to highlight the fascinating discoveries being made even while species go extinct faster than they can be identified. “The last vast unexplored frontier on Earth is the biosphere,” said Quentin Wheeler, president of the College of Environmental Science and Forestry. "We have only begun to explore the astonishing origin, history, and diversity of life."

Undiscovered species contain undiscovered wealth of all descriptions, Wheeler added. "Among the remaining 10 million are irreplaceable clues to our own origins, a detailed blueprint of how the biosphere self-organized, and precious clues to better, more efficient, and more sustainable ways to meet human needs while conserving wild living things."

The Why Files cherry-picked seven of the top-10…

Images and some text courtesy of International Institute of Species Exploration, State University of New York College of Environmental Science and Forestry.

Odd critters

A living fossil, Dendrogramma enigmatica could represent a new phylum; the photo was taken after the specimen shrank in storage. Credit: Jørgen Olesen, University of Copenhagen

In 1986, a 1,000-meter deep ocean trawl near Australia yielded 18 disks attached to short stalks -- and more questions than answers1. Dendrogramma enigmatica (savor that name!) and the close relative D. discoids are 11 millimeters across whatchamacallits. They have a mouth on the disk, but there are signs of neither propulsion nor attachment to the ocean floor. The new genus resembles phylum Cnidaria (jellyfish, corals, sea anemones and hydras) and phylum Ctenophora (comb jellies) but there's nothing definitive -- the DNA did not survive storage in formaldehyde and alcohol. The head of the scientific squad wrestling with these oddities, Jørgen Olesen of the University of Copenhagen, has been hesitant to create a new phylum for them, but suggests they represent "an early branch on the tree of life, with similarities to the 600 million-year-old extinct Ediacara fauna."

Anzu wyliei: Fashion-forward dino – or the "chicken from hell"?

Life reconstruction of the new oviraptorosaurian dinosaur discovered in western North America. Anzu wyliei lived about 66 million years ago. Illustration: Mark A. Klingler, Carnegie Museum of Natural History

With hollow bones, a parrot-like beak, and of course those high-style feathers, the crested dinosaur Anzu wyliei was part of the "bird look" that became so popular with the high-flying set. Three specimens were discovered in the Hell Creek Formation in South and North Dakota, United States, in 19982. About 3.5 meters long and weighing 200 to 300 kilograms, the "chicken from hell" ate plants, small animals, even eggs over easy. A contemporary of T. rex, Anzu wyliei made nests and guarded its eggs as they hatched -- or so paleontologists believe. Aside from those stunner looks, the "chicken" is valued for its relatively complete specimens, which helped untangle the ancestry of its relatives.

Crazy critters

Torquigener albomaculosus: The aquatect of circles

The discovery of a new species of pufferfish, Torquigener albomaculosus3 solves a two-decade marine mystery. Male fish make these precise, 2-meter-diameter spawning nests by swimming and wriggling in the seafloor. The ornate circles begin as girl-getters rather like the nest of the bowerbird, but the ridges and grooves also reduce currents at the center to protect the eggs from turbulence. Underwater photographer Yoji Okata first observed this artistic aquatic architecture.

Photographs: Yoji Okata

Deuteragenia ossarium: Wasp mounts chem-war defense!

Protection also matters if you're a wasp casting your genetic future to the winds -- in other words, depositing your eggs. The daintily named bone-house wasp, a half-inch-long top-10 standout, has an unusual tactic: pack the brooder house with chemical repellent so predators will turn up their noses at your matrimony. The Deuteragenia ossarium wasp builds multi-cell nests in hollow stems and deposits one spider in each cell to nourish her young as they develop. She seals each cell with a soil wall, kills a spider for the next cell, then fills the last cell with up to 13 dead ants. The wasp is the first animal known to create such a chemical barrier to a nest, and it works: Deuteragenia ossarium, found in Gutianshan National Nature Reserve in eastern China, has significantly lower parasitism rates than similar cavity-nesting wasps4.

A Deuteragenia ossarium nest shows the unique nest-protection strategy (dead ants in the left chamber), and developing wasp larvae in the other four chambers. Photograph: Merten Ehmig

Cebrennus rechenbergi: Rollin' and tumblin'!

Stills of the cartwheeling spider in mid-tumble in Erg Chebbi, Morocco by Ingo Rechenberg, Technical University Berlin

A newly-named acrobatic arachnid5 living among Moroccan sand dunes has found a new use for its eight long legs: why run from danger when you can cartwheel? In the face of a threat, the gymnastic Cebrennus rechenbergi lurches up, then throws its body over into a cartwheel, doubling its speed. Tough terrain? No problem: While other spinning spiders only roll downhill, C. rechenbergi can maneuver up, down and around the desert dunes. Here's the most outlandish aspect of this defensive move: the spider propels itself towards the threat, not away. With few places to hide among the barren dunes, C. rechenbergi embodies the mantra that the best defense is a good offense. The spider's discoverer, Ingo Rechenberg, is a bionics expert fascinated by the ingenious mobility of desert species. Rechenberg has since designed robots that mimic the spider’s motion, which could be useful for exploring Mars.

Odd lessons

Tillandsia religiosa: A flowering beauty, hiding in plain sight

Mexico’s Christmas season is a parade of elaborate decorations, focused, both culturally and visually, on the nativity scene, or “nacimiento.” Intricate altars depicting the birth of the Child Jesus are often adorned with native Spanish moss and beautiful epiphytes (rootless plants) known as bromeliads. One bromeliad long appreciated in the Central highlands, and a frequent component of altar displays has, until now, escaped the scientific compulsion to name species. Tillandsia religiosa6 (got to love that name!) inhabits rocky outcrops in deciduous, coniferous and cloud forests within a narrow band of elevation from 1,800 to 2,100 meters in Morelos State. T. religiosa, with its hard-to-miss rosy-red flowers, is a humbling reminder that discovery may lurk beneath our noses.

Phobaeticus chani: Stalking the Giant Sticks

In a testament to stupendous camouflage, an insect in the giant stick family has only now been noticed7 by entomologists in Vietnam. While Phryganistria tamdaoensis may not be the world’s longest stick (that title belongs to Phobaeticus chani), it is 9 inches long! So how DID such leggy characters elude the eyes of science for so long? It's not just that uncanny, stick-similitude: Giant sticks are slow-moving and drop motionless to the ground when disturbed; a better stick impression there is not. Science’s slowness to find these giant insects is compelling evidence that more remain to be discovered. Keep your eyes on the sticks!

How climate drives bird migration

Pine siskins, a species of seed-eating boreal bird, will spend some winters in the pine, spruce and fir forests of Canada, and then arrive at bird feeders much farther south during others. Ornithologists suspected the irregular migrations tracked oscillating climate patterns, but a direct link was elusive, until now.

Why do certain birds suddenly leave their winter territory -- sometimes in the middle of winter? The more familiar, "seasonal" migration is triggered by changes in day length, and birds tend to fly south in winter. But what sparks this "facultative" migration, with its dense "irruptions" of hungry birds that often fly hundreds of kilometers in various directions?

During an irruption, the pine siskin may abandon its wintering turf in Canada and fly south, east or west across Canada's vast boreal forest. Siskins in the Appalachian Mountains may fly northeast or southwest, paralleling the mountain range.

"This happens, in some cases, every other year, or every few years," says Benjamin Zuckerberg, an assistant professor of wildlife ecology at the University of Wisconsin-Madison. "In the 'superflight' years, you get multiple species irrupting out of the boreal forest and showing up at feeders, in really large numbers."

Reading hunger

Hunger is a clue to these migrations, and the pine tree's cycles of fruit production -- called "masting" -- explains that hunger. In a "mast" year, the trees produce a heavy crop of seeds and the birds reproduce well; in lean years, the crop may be nearly nil, and the birds must leave or starve.

The coniferous forests of boreal Canada and northern U.S.support many populations of the pine siskin with year-round seeds. Occasional “swings” in the North American dipole, though, lead to irregular migrations of pine siskin to more southerly forests and bird feeders.

Mast years, in turn, usually follow a warm and/or dry year, and so climatic swings set the schedule. And masting, by leading to those hungry years, could explain facultative migration.

To explore what drives facultative migration, a new study1 in the Proceedings of the National Academy of Sciences, based on citizen-scientist observations at bird feeders, viewed climate in terms of "dipoles." These contrasting regions (of high and low temperature, or heavy and light precipitation) affect seed production and therefore bird populations and migration.

And that helps explain why pine siskins are common in some years and absent in others, and why they occasionally throng feeders where they are seldom seen. The math was complicated, but the bottom line was that climate explained 58 percent of the north-south movement, and also 58 percent of the east-west movement.

Curiously, the patterns of precipitation and temperature in the dipoles "stem in part from thunderstorms in the Asian monsoons during the warm season," says first author Courtenay Strong, an assistant professor of atmospheric sciences at the University of Utah. "That creates atmospheric wave patterns that cross the Pacific and contribute to the dipole."

Coniferous trees, like this cedar, often brim with seeds and nuts during “mast” years marked by favorable climate. Pine siskins will leave their usual stomping grounds to follow productive trees.

Love those amateur scientists!

Meteorologists and climate scientists are used to wading knee-deep in data, but the citizen-science movement is helping envious biologists catch up. The irruption study, for example, rested on more than 2 million amateur observations of pine siskins through Project FeederWatch.

"Citizen science is absolutely critical for being able to document these patterns," says Zuckerberg, another author of the PNAS paper. "It plays right into the strengths; it's a very noticeable biological phenomenon, people are logging at their feeder and seeing dozens or hundreds of siskins descending. They know when an irruption year is taking place."

Although citizens and scientists have long recorded the signs of spring, "Documenting, quantifying the nature of irruptions is something we have always wanted to do in ecology," says Zuckerberg. "This is the first time we have been able to document this, and could disentangle the role of climate on the irruptions."

The study also entailed a different perspective for climate scientists, who usually focus on how weather patterns affect people. "When we start looking at problems that affect birds, we are looking at phenomena that we have not paid as much attention to in the past," Strong says.

Because the dipole phenomenon seems to be increasing as the climate changes, the new study "offers a lot of implications for seeing how climate change is going to affect the boreal forest and its constituent species," Zuckerberg says.

Although we can understand the "push part" (why birds fly to flee a territory that can't feed them), how do they locate better habitat? "The pull part is tougher to get a handle on," Zuckerberg agrees. "Are they sampling the environment as they make the sojourn? Are they cueing in on other birds? Those are certainly possibilities."

First animal ancestor discovered in deep mud!

The evolutionary jump from prokaryotic to eukaryotic cells has eluded scientists searching for evidence of intermediate single-celled life. Discovery of Lokiarchaeota, the closest known prokaryotic relative of eukaryotes, confirms that eukaryotes evolved from Archaea.

“Prokaryotic,” from the Greek pro- (before) and karyon (a nut or kernel), refers to cells that lack a nucleus for housing genetic material. Archaea are prokaryotes equipped to thrive in the harshest environments, like volcanic hot springs or the ocean deep. Eukaryotes (eu- = “well”), on the other hand, have nuclei and other membrane-bound organelles that support the diversity of complex life, from amoebas and fungi to redwoods, to humans.

Genealogists around the world were jealous-green at yesterday's announcement that a single-celled organism living 2.5 kilometers under the ocean off the coast of Norway represents a long-sought relative of all cells with a nucleus -- the eukaryotes.

This distant relative, formally Lokiarcheota, barely reproduces and scrounges leftovers after the microbes above it have eaten their fill.

Forgive the cliché, but Loki is a game changer. For many years, biologists have tried to trace the first nucleus-bearing cells to the simpler cells that came before -- but with little or no evidence either way, the result was mainly academic discord.

Now we know: Genetics prove that Loki, although not yet sophisticated enough to have a nucleus, had the same ancestor as eukaryotes -- as us.

That's a big deal, as Loki is a member of the ancient microbial domain Archaea. Many have thought that eukaryotes descended from Bacteria -- the other giant domain of nucleus-free microbes.

Meet your cousin: Resident of deep, cold ocean mud joins the family!

Ancestral attack

We complimented corresponding author Thijs Ettema, an associate professor of cell and molecular biology at Uppsala University in Sweden, on discovering our ancestor, but he clarified that it's not an ancestor: "This is the cousin of the eukaryotes, from 2 billion years ago, give or take half a billion years."

We remained impressed: Here was an Archaea that, like all Archaea, lacked genes for a nucleus, yet it has genes for complex structures that were until now considered unique to eukaryotes.

Lokiarcheota is named for its source in the North Atlantic, in a 2,500-meter trough near Loki’s Castle, an undersea mountain. The new Archaea carries mythical undertones of the shape-shifting Norse god Loki, suitable to an organism that blurs the line between prokaryote and eukaryote.

Although little is known about how Loki made a living (only its genes are known), this distant ancestor does not live large. "Microbes that live on the ocean floor thrive on anything that might fall down," Ettema told us. "Since Loki was a meter deep in the sediment, all these microbes above it are able get to those nutrients first. It was eating whatever was left."

Living near 0°C, Loki may divide only once in a decade.

Having identified a new organism that we share an ancestor with, Ettema cautions that "We are looking at a modern-day organism that is not identical to our common ancestor." Two billion years ago, "Earth was a completely different world, there would not have been a lot of oxygen in the atmosphere or ocean; it was not an environment that was very friendly to modern organisms."

"Loki was chilling out in the ocean floor sediments, in an environment where there was not a lot to eat."

Genetic ju-jitsu

Lacking any specimens, Ettema's group relied on metagenomics -- the systematic construction and comparison of genes. The process starts with "shotgun sequencing," a quick method for reading one organism's genome from samples that may contain hundreds of microbe species:

DNA is isolated and cut into short strands.

Using high-speed sequencing, the letters in each strand are read (for example, TATTTACGCGATTC TGAGAGTTC) and CTTGACATTATTTACGCGATTC).

Identical sections are digitally overlapped to make longer strands and eventually the full genome. (In the example, the identical bold sequences overlap, showing where the fragments join.)

Organisms are identified through a variable stretch of RNA called 16S, which "is a marker used worldwide to answer the question, ‘Who is there?’" says Ettema. "It's a sort of barcode."

High-intensity sequencing and computing produced a microbe with an ancient relationship to all higher organisms.

Like us, Loki descended from an ancient bridge between prokaryotic and eukaryotic life that lived about 2 billion years ago. Loki’s genetic material resembles eukaryotic genes, but the organism has no nucleus, so this deep-sea critter grew from a microbe that connects simple and complex cells.

The Why Files

Read the genes, read the story

Loki was an Archaea, but it carried many genetic signatures of eukaryotes. "We identified about 100 genes that Loki uniquely shares with eukaryotes, that were considered unique to them," Ettema says.

These genes

form parts of ribosomes, which make proteins;

make actin, a protein that shapes cells through a structure called the cytoskeleton;

form vesicles, containers that transport and store chemicals; and

take up objects -- even organisms -- from the environment. This could have allowed eukaryotes to consume the microbes that became mitochondria -- internal energy machines.

And thus Loki is part of the long lineage of eukaryotes -- people, plants, fungi and the rest -- and all of that descended from Archaea. "We have known very little about the timing of the events surrounding the development of eukaryotes," Ettema says. "Now we know that some amount of cell complexity occurred before the nucleus or the organelles came into play. There was already a toolkit."

Bombardier beetle spray-bottle explained at last!

Photograph of a bombardier beetle (Brachinus elongatulus) in action. The many species of Bombardier beetles inhabit moist ground layers of temperate forests and grasslands around the globe, with B. elongatulus calling Eastern Europe home. They feed on small insects nocturnally while keeping predators like tree frogs at bay with their explosive hind parts.

In a development that's sure to catch fire in the growing market for organic self-defense sprays, a group at MIT has figured out how the bombardier beetle produces its hot, irritating defensive spray. Squirting across a few centimeters at close to water's boiling point, the spray long ago caught the eye of curious biologists.

Members of the "Brachinini" tribe -- a sub-group of the 1,400 species of bombardier beetle -- defend themselves by spraying a toxic brew ready-made for the occasion. In this week's Science, we read the structural details behind this bio-chemical warfare.

"We have beetles with an explosion inside the body, and they don’t die," says first author Eric Arndt, a Ph.D. student in material science and engineering at MIT. "How? People have studied this for a long time, with most of the focus on the chemistry of explosion and the behavior of the beetles. There was very little mechanistic work on what happens inside the beetle."

The spray is produced by a complicated gland at the hind end, Arndt says. "I got this idea: How about we use this half-billion dollar machine and take high-speed video to see the explosion?"

Arndt is referring to the Advanced Photon Source at Argonne National Laboratory, which, he says, "pioneered live-imaging of centimeter-sized animals; it's been used to see how insects breathe, how butterflies drink, and now how beetles defend themselves."

The work by Arndt and his advisor, Christine Ortiz, shows a rapidly pulsing spray created by a series of explosions created when a chemical called the reactant is exposed to a catalyst inside a reaction chamber. That chamber turns out to be highly engineered by evolution to make, heat and shoot the spray while protecting the beetle from its own chemical weapon.

The abdominal squirt-gun of the bombardier beetle has striking similarities to a pulsejet, a propulsion system that fires in pulses. Roll over graphic to see the pulse jet that powered the first cruise missile, the German V-1 "buzz bomb" that attacked London in 1944.

Pulsation sensation

The basic trick of the Brachinus elongatulus beetle under study was already known. It works like a pulse jet, with the energy released in a staccato of small explosions, each containing about 6 micrograms of toxic fluid.

Pulsing produces a cascade of benefits, Arndt explains. "High spray velocity reduces latency, so you get your message to the predator quicker. Because pressure is proportional to the amount of spray, the pressure is lower, so they don’t need the reaction chamber to be so strong, and they don’t have to spend as much energy building the structure."

As a fringe benefit, the beetle has better aim because the lighter shot reduces recoil.

The most surprising finding, Arndt says, is a flexible reaction chamber. "You would expect for an explosion chamber that you don’t want it to deform, particularly inside an exoskeleton that does not have a lot room to give."

The deformation of the reaction chamber, however, helps regulate the pulses, by closing the valve that allowed reactant to enter the chamber, which protects the beetle from the hot, toxic spray it creates. Then, after the spray jets out, the pressure drops and the valve opens, so more reactant enters the chamber.

Meet the cuticle

Why would a material scientist be interested in a beetle's toxic spray if he doesn’t prey on bombardier beetles? Because the entire assembly of reactant reservoir, valve, reaction chamber and nozzle is a one-piece structure made of a natural material called cuticle -- the same stuff that builds an insect's external skeleton.

"Insect cuticle is amazing, and these beetles use it quite cleverly," Arndt says. Think of plywood -- where the wood fibers are stacked crisscross style to balance their physical properties and make a material that's more or less equally strong in all directions.

Synchrotron X-ray video of pulsed explosions inside bombardier beetle defensive glands while the beetle ejects its defensive spray, recorded at 2,000 frames per second, played back at 25 frames per second. Pulsating bright regions are vapor pockets inside the glands; each pulse (enlargement and blurring of vapor pocket) corresponds to an explosion.

E. Arndt, W. Moore, W.-K. Lee, C. Ortiz

"The work explains how internal explosions, high-repetition rate pulsed-jets and liquids hotter than boiling water can all be generated and tolerated by living tissues," says Pupa Gilbert, professor of physics and chemistry at the University of Wisconsin-Madison. "These are amazing feats of bioengineering, which evolved to defend the beetle from its enemies," says Gilbert, who studies nacre (mother of pearl). "I just hope I will never cross one of these beetles!"

Chitin, the fibrous material in an insect's exoskeleton, is even better. The nanometers-in-diameter chitin fibers "are stacked in layers, and each layer is rotated slightly, so no matter which direction you stretch, it has same mechanical properties," Arndt says.

The spray gland is an outgrowth of the exoskeleton, Arndt says. "It goes from the stiff exoskeleton to an exit channel that is half flexible and half very stiff, to a reaction chamber that is mostly stiff, but has specific areas that are thin and flexible, to a reservoir that is flexible, and to a valve that is made of a rubbery material. It's one thing, but the material properties vary all the way along."

By varying the direction of the chitin fibers, and altering protein and water content, insects "achieve a level of intimate control of material we’d love to achieve," Arndt says.

"The cuticle exoskeleton is a key to the success of insects," says Arndt, "which arguably are the most successful organisms on the planet because they have this exoskeleton that provides protection but allows them to get around and regulate water content."

Cuticle also houses and protects spiders and mollusks -- the crabs, lobsters and bivalves, and is found in their various fangs, pincers and shells.

Biomaterials in general are eminently effective, Arndt says. "A lot of work is going on to understand how animals make these materials: nacre [mother of pearl], insect cuticle, wood, bone. These are very high performance materials, because animals have intimate control over the nanostructure as they are created. As scientists we can't do that."

Drought + food = instability?

The California drought is cinching down: On April 1, Governor Brown announced the first mandatory restrictions on water usage in the history of the Golden State.

A winter with disastrously little snowfall after four years of drought forced the Governor's hand. The 25 percent cut-backs on residential usage come on top of long-term clampdowns on water for farming, which absorbs 80 percent of the state's supply.

In the midst of a drought that's being called the worst in a generation, California is speeding up a $1-billion package of water-infrastructure improvements.

And that got us to thinking. California grows, with help from a vast system of irrigation, the majority of many fruits and vegetables eaten in the United States. Drought has already cut production, and more is likely to come.

In 2013, the International Disaster Database reported that, drought killed more than 11 million people and affected more than 2 billion between 1900 and 20111.

However, as we'll see, drought seldom acts alone: Foolish or cruel government policies, and many other factors, can multiply the death toll. Let's look at some examples.

Severe droughts are affecting much of California, and parts of Nevada and Texas. ROLLOVER GRAPH to see 100-year history of drought in California. Positive values of the Palmer Drought Severity Index represent wetter-than-average conditions. A value between -2 and -3 indicates moderate drought, -3 to -4 is severe drought, and -4 or below indicates extreme drought.

Syria's suffering: Drought and civil war

As the Syrian civil war continues to chew up lives and spit out refugees, we hear evidence linking the uprising against the Assad Regime that started during the 2011 "Arab Spring" to the 2007 - 2010 drought -- and to global warming.

Those conclusions emerge from a new study2 by Colin Kelley of the University of California at Santa Barbara. "We found a very clear signal of climate change over the Eastern Mediterranean and the Fertile Crescent," Kelley told us.

Winter brings rain in Syria's Mediterranean climate, but the winter of 2008-09 was the driest in the last 100 years, damaging the domestic wheat crop. From climate models and weather data, Kelley and his colleagues concluded that climate change had doubled or tripled the odds of the severe drought.

Crop failures caused by three parched years in a row forced about 1.5 million farmers into the cities, joining almost as many refugees from the Iraq war. Between 2002 and 2010, Kelley says, Syria's urban population rose by 50 percent. "The government did little to ease the suffering of the displaced population," which became instrumental in the opposition to dictator President Bashar Assad.

Despite its semi-arid climate, Syria has enough rain to support substantial agriculture, albeit limited to the North and near the Mediterranean coast. But drought wreaked havoc on croplands with tight water resources between 2007 and 2010. Roll over to see Syrian rebels mounting a tank after nationwide protests against President Bashar al-Assad erupted into civil war in 2011. Drought-related crop failure and urban migration added stress to overcrowded cities, precipitating the continuing Syrian Uprising.

Droughts have forced past migrations, but population made a difference this time, Kelley says. "In a lot of this region, the population 40 or 50 years ago was a small fraction of what it is today, and that made a stronger demand for water."

Kelley concedes that we can't be sure climate change, acting through drought, caused the Syrian uprising. "It's impossible to know what would have happened in the absence of severe drought and without this huge influx of agricultural refugees. You could make the argument that it would have happened anyway. Syria was the last of the Arab spring revolts, and it already had overcrowding. We make the case that the drought pushed them over the threshold of resilience."

Egypt's agony

Egypt, another Middle-Eastern state trapped between vast deserts, also faced drought-related difficulty during the Arab Spring of 2011. In that year, growing conditions in China, Ukraine, Russia, Canada and Australia contributed to a wheat shortage, and the price doubled.

Egypt was then ruled by the aging autocrat Hosni Mubarak. Densely populated, corrupt and poor, it was the world's largest importer of wheat and did not have wheat or cash reserves to deal with the price spike. The rising price of bread fed popular discontent, leading to Mubarak's overthrow and the election of a Muslim Brotherhood government under President Mohammed Morsi. (Morsi was ousted in July, 2013 by the military junta that now rules Egypt. In April, 2015 he was sentenced to 20 years in prison for directing the arrest and torture of prisoners.)

Egypt is the world’s largest importer of wheat, so declines in wheat exports from countries like China and Russia have devastating downstream effects on Egypt’s bread markets. Rollover to see an Egyptian man wielding a pita bread during a Cairo protest against cheap wages and dear bread.

Troy Sternberg of Oxford University, who has studied3 Egypt during this period, does not argue that drought alone caused the Egyptian edition of Arab Spring. "We think of drought and climate change as threat multipliers. They are not usually the main cause of famine, but they show the fragility of the system. You push it somewhere, and it can break down, and it usually starts with poor government policy."

Corruption is always a factor in Egypt, Sternberg adds. "Mubarak's friends and relatives, the army, would profit from wheat imports, and money left country when the protests happened."

Before the drought, Egypt, prodded by the International Monetary Fund and World Bank, had converted some portion of its limited supply of farmland to higher value export crops like mangoes and flower, Sternberg says. "When you give up self sufficiency, you better have a plan B, and Mubarak had no plan B."

China: Lessons from a history of drought

"Brave the wind and the waves, everything has remarkable abilities, 1958 [translation]" 1958 - 1961: The Communist Party of China launched a campaign to transform the agrarian nation into a socialist industrial powerhouse. Propaganda artwork like this poster painted the Great Leap Forward as a vibrant, cooperative ride (note the rocket-rider in the sky?) to enter the modern era, but in reality, many millions died of famine.

Things were quite different in China, by far the world's biggest wheat producer, in the same period. China's government bolstered the food supply by expanding irrigation, trucking in water, buying large amounts of wheat on the global market, and even tolerating dissent. "China used its own versions of Twitter and Facebook as political-pressure release valves," says Sternberg.

Events within the memory of China's leaders had shown the danger of drought and famine. Between 1950 and 1990, natural disasters caused an 11.6 percent reduction in China's crops, with about 86 percent of the falloff was due to droughts and floods4.

The shortage peaked during the "Great Chinese Famine" (1959 to 1961), which showed how government policies turned a rainfall shortage into a catastrophe. In 1958, under the reign of the Communist leader Mao Zedong, the government initiated the "Great Leap Forward," which centered on a compulsory movement "back to the countryside" by city people who were supposed to establish collective farms and joyfully feed the people.

To squeeze more food from the farms, the government set unrealistic goals and goaded hungry, resentful farmers. "The line was that 'There was a surplus, why doesn’t your area have enough food? It's obviously your fault,'" Sternberg says. With production over-estimated, peasants were required to ship more grain than they could afford.

Estimates of the Great Chinese Famine's death toll range from 15 million to 45 million. "It shows the power of a government, if it gets the policy totally wrong," Sternberg adds.

China: Collapse of the Ming Dynasty

China had plenty of earlier experience with the skein of connections between drought to famine. To tease apart the interplay of weather with famine, "political corruption, fiscal deterioration, food crises, popular unrests, border crises and wars," Chinese scientists5 examined detailed records on climate and history from the Ming Dynasty (1368 - 1644), and saw a big role for drought and cold weather in a long decline that started in the mid-1500s and culminated in a successful peasant revolt.

These researchers concluded that severe drought, frost and flood caused crop failures that shut down 2.9 million hectares of farms feeding garrisons defending against Mongol enemies north of the Great Wall. Finances deteriorated as the military absorbed 76 percent of the budget from 1570 to 1589. Between 1627 and 1643, the most severe drought since 500 AD helped trigger a peasant uprising that brought down the dynasty in 1644.

As the climate changes…

The past is ominous enough. What about the future? There are signs that climate change will damage food production by raising temperatures, spreading diseases and pests, and changing rainfall. Insufficient rain causes drought, but heavy rainstorms that seem to be accompanying climate change can cause runoff and erosion without effectively recharging groundwater.

The great American Dust Bowl

Droughts are no stranger to the American West, and the king of them all, in recorded history, is called the Dust Bowl. The droughts came in three bursts. In 1934, 1936 and 1939 - 40, rainfall plummeted, and high temperatures and strong winds whipped across the Great Plains. Years of heedless farming had left topsoil vulnerable to erosion, and the high winds blew dried soil into billowing dust storms. Crops in the Great Plains were decimated, compounding the Great Depression for many families. With nothing left, countless farmers left the Dust Bowl states in search of better climate and fortune. As depicted in The Grapes of Wrath (John Steinbeck), a great many went to California.

Evidence linking climate change to drought and reduced plant productivity comes from a recent study7 of 2000-2009, the hottest decade on record. The study looked at net primary production, or NPP, which measures the conversion of the carbon in carbon dioxide into sugar through photosynthesis -- the first step of practically every food chain. Satellite measurements of leaf area and photosynthesis showed a 1 percent NPP loss in the decade, caused largely by these droughts:

2000: North America and China

2002: North America and Australia

2003: Europe

2005: Amazonia, Africa and Australia

2007-2009: large parts of Australia

In Syria, hot weather dried the soil, and groundwater was overtapped for farms. "In the past, they used groundwater as a buffer against dry years, but because of the population increase and the drying trend, they were pulling even more water out of the ground," Kelley says. California and the Southwest "are in a very similar situation. Groundwater has been running out, and there is less precipitation."

Nobody is anticipating a revolution in California, but the state's incessant growth (the population is now 39 million), may have to slow. Already, some crops are being moved to wetter areas, cities are learning to recycle wastewater and desalinate seawater, and residents are urged to replace thirsty grass with desert plants.

"The whole Middle East is the biggest food importer in the world," says Sternberg, and now that food is increasingly a global commodity, the long-distance effects of drought become even more grave. "If I were Saudi, I would worry about the California drought. If a production area for an important cereal has a 'climate event,' it’s as important as if it happened in your own state."

It's all a part of globalization, Sternberg says. "We talk about the movement of money, people, products across the globe, so it should not be a surprise that this can take place with climate and other drivers. Once you have interlocking networks, this is going to happen."